1. Field of the Invention
The invention relates to a receiving part for a retaining component of a vertebral column implant.
2. Description of Prior Art
With vertebral column implants there exists often the object of supporting certain vertebra of the vertebral column, of creating a tension between the vertebra or a compression in order to retain or change a relative position. For this purpose, suitable means are connected to the vertebrae which are subsequently described as retaining components and may be connected to one another by connecting means. As retaining components, there may be e.g. so-called pedicle screws which are screwed into the pedicle of the vertebrae. The head of the pedicle screw is either annular or fork-shaped. With annular pedicle screw heads e.g. a distraction rod is guided through and is fixed on both sides of the head with the help of a nut. With fork-shaped heads, it is known in the inside to provide threaded sections for a set screw with which a previously inserted distraction rod or likewise may be fastened.
A similar receiving part for a distraction rod or likewise is also known for hook-like retaining components, for example with so-called lamina hooks or pedicle hooks which are hooked into the corresponding vertebrae parts.
With fork-shaped receiving parts, there is the danger that on exerting a suitable pressing force on the distraction rod or likewise the arms of the fork-shaped part are bent apart by which means the fixation is compromised or even eliminated. It is known, for example, to counteract this in that a lifting eye bolt or nut is screwed on the outside around the receiving part in order to prevent the arms from bending apart. A so-called cap bolt has a similar effect, this bolt overlaps the receiving part at the open end and includes a centrally located peg-like section projecting into the recess of the fork-like part for fixation e.g. of a distraction rod.
From U.S. Pat. No. 4,946,458, it is also known to equip the end, on the head side, of a shank of a pedicle screw with a spherical bearing surface which is fastened in a corresponding bearing section of the head. By way of this, the shank of the pedicle screw may assume any angle with respect to the screw head. It has, however, been shown that it causes problems in securely fixing the relative position of the pedicle screw on the one hand and the receiving part or the head on the other hand.